1. Technical Field
The present invention relates to an optical scanner for allowing a laser beam emitted from a light source to cross an fxc2x7xcex8 lens in a copying machine, a laser printer, or the like. In particular, the invention relates to a technique for preventing a plate-shaped bracket of an fxc2x7xcex8 lens assembly from interfering with a laser beam emitted from the light source.
2. Related Art
Conventionally, as disclosed in Japanese Patent Application Laid-Open No. 11-258532 (1999), in a copying machine, a printer, or the like in which a laser beam is scanned so as to form an image, a machine, in which laser beam is emitted from a light source is allowed to cross an axial line of an fxc2x7xcex8 lens so that its structure can be made compact, is known. FIG. 5 shows one example of an optical scanner to be used in such a copying machine or the like. In the optical scanner shown in this drawing, a laser beam La emitted from a light source 1 such as a laser diode is transmitted through a collimating lens 2 so as to be formed into a parallel light beam and is formed into a linear spot by a cylindrical lens 3. Thereafter, the beam passes through between a pair of fxc2x7xcex8 lenses 6 from below and is reflected by a first reflection mirror 4 so as to enter a rotatable polyhedral mirror 5. The laser beam La, which is deflected by the rotatable polyhedral mirror 5 which rotates at a constant speed, is transmitted between the paired fxc2x7xcex8 lenses 6, and is reflected by a second reflection mirror 7 and a third reflection mirror 8 so as to form an image on a scanning surface 9. In this case, the fxc2x7xcex8 lenses 6 have a function for making the moving speed of an imaging position in a horizontal direction on the scanning surface 9 to be constant.
In the optical scanner, in order to prevent occurrence of so-called xe2x80x9cghostingxe2x80x9d in an image, an optical axis is generally tilted in an up-and-down direction. In other words, in the optical scanner shown in FIG. 5, the laser beam La emitted from the light source 1 is acclivitous, a laser beam Lb reflected by the first reflection mirror 4 is declivitous, a laser beam Lc reflected by the rotatable polyhedral mirror 5 is declivitous, and laser beams Ld and Le reflected by the second and third reflection mirrors 7 and 8 are declivitous.
The fxc2x7xcex8 lenses 6 are conventionally fixed to a bottom plate of a housing of a copying machine, for example, by bonding. However, if defects occur in the fxc2x7xcex8 lenses 6 or another arrangements, the entire copying machine should be discarded. For this reason, in recent years, the fxc2x7xcex8 lenses 6 are fixed to the plate-shaped bracket to be a sub-assembly so that when a defect occurs in the fxc2x7xcex8 lenses 6, only the sub-assembly of the fxc2x7xcex8 lenses 6 need be discarded. More specifically, the fxc2x7xcex8 lenses 6 are bonded to an upper surface of the plate-shaped bracket, and the plate-shaped bracket is fixed to the bottom plate of the housing by a screw.
However, an up-and-down distance between the laser beam La emitted from the light source 1 and the laser beam Lc passing through the lower side between the fxc2x7xcex8 lenses 6 is set to be fairly short in order to reduce the thickness of the device. Since the laser beam La is tilted, its optical path is interfered with by the plate-shaped bracket for supporting the fxc2x7xcex8 lenses 6, and thus there arises problems in that the laser beam La does not form an image on the scanning surface 9 or even if it does form an image, an electrostatic latent image is not formed.
It is an object of the present invention to prevent a plate-shaped bracket of an fxc2x7xcex8 lens assembly from interfering with a laser beam emitted from a light source in an optical scanner in which the laser beam emitted from the light source is allowed to cross an fxc2x7xcex8 lens.
The present invention provides an optical scanner comprising a light source, a reflection mirror, deflection device, and an fxc2x7xcex8 lens fixed to a plate-shaped bracket. The optical scanner is characterized in that a luminous flux emitted from the light source is guided to the deflection device by the reflection mirror and the luminous flux deflected by the deflection device is guided to the fxc2x7xcex8 lens, a light source optical path from the light source to the reflection mirror is arranged to be tilted with respect to a plane which is drawn by an optical axis of a scanning optical path led to the fxc2x7xcex8 lenses deflected by the deflection device, and the light source optical path is arranged on one side across the plane drawn by the optical axis of the scanning optical path, and the plate-shaped bracket of the fxc2x7xcex8 lens is arranged on the other side.
According to the optical scanner having the above structure, since the light source optical path from the light source to the reflection mirror is arranged on one side across the location drawn by the optical axis of the scanning optical path and the plate-shaped bracket of the fxc2x7xcex8 lens is arranged on the other side, the plate-shaped bracket is separated from the light source optical path and does not interfere with it.
As mentioned above in the present invention, the fxc2x7xcex8 lens is fixed to another plate-shaped bracket which is not used for the housing of the optical scanner so as to be constituted as the fxc2x7xcex8 lens assembly (subassembly). In a preferable form of the present invention, the light source, the reflection mirror, and the deflection device are provided in the housing, and the plate-shaped bracket is attached to the bottom surface of the housing with an interval. In this case, a luminous flux emitted from the light source has an acclivity with respect to the bottom surface of the housing, and the fxc2x7xcex8 lenses are fixed to the lower surface of the plate-shaped bracket. This provides an advantage in that the upper side of the fxc2x7xcex8 lens is covered by the plate-shaped bracket and dust hardly adheres to the fxc2x7xcex8 lens. Moreover, when the upper side of the fxc2x7xcex8 lens is covered by the plate-shaped bracket, it appears that the lens is housed in the housing, thereby providing a compact structure. Therefore, the functions are diversified in such a manner that a harness for wiring is allowed to pass through the upper surface of the plate-shaped bracket or other parts are attached.
More specifically, the plate-shaped bracket is attached to a boss which stands on the bottom surface of the housing by a screw, and a space is provided between the plate-shaped bracket and the bottom surface of the housing. Moreover, two fxc2x7xcex8 lenses, for example, are fixed to the lower surface of the plate-shaped bracket by a device such as bonding, and a luminous flux such as a laser beam emitted from the light source crosses between the fxc2x7xcex8 lenses from the top view, for example, at the lower side of the plate-shaped bracket. The present invention can be applied to the case of one fxc2x7xcex8 lens, and this includes the case where a luminous flux crosses the fxc2x7xcex8 lens from the top view and the case where the luminous flux crosses front or rear positions of the fxc2x7xcex8 lens.